The present invention relates to a radiation image erase unit for erasing remaining radiation image information from a stimulable phosphor sheet by exposing the stimulable phosphor sheet to erasing light emitted from an erase light source, and more particularly to a radiation image erase unit for use with stimulable phosphor sheets which includes an air blower means for cooling the stimulable phosphor sheets that is disposed in a casing surrounding the erase light source.
There has in recent years been proposed a radiation image recording and reproducing system in which an irradiation image of an object can be produced by using a stimulable phosphor. The stimulable phosphor, when exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays, or ultraviolet rays, stores a part of the energy of the radiation. When the stimulable phosphor exposed to the radiation is exposed to stimulating rays such as visible light, the stimulable phosphor emits light in proportion to the stored energy of the radiation.
The radiation image recording and reproducing system employs such a stimulable phosphor. More specifically, the radiation image of an object such as a human body is stored in a sheet having a layer of stimulable phosphor (hereinafter referred to as a "stimulable phosphor sheet" or a "phosphor sheet"), and then the stimulable phosphor sheet is scanned with stimulating rays such as a laser beam to cause the stimulable phosphor sheet to emit light representative of the radiation image. The emitted light is then photo-electrically detected and converted to an electric image signal which is processed to reproduce a visible image on a recording medium such as a photographic film material or on a display unit such as a cathode ray tube (CRT). The aforesaid radiation image recording and reproducing system is disclosed in U.S. Pat. No. 4,258,264 and Japanese Laid-Open Patent Publication. No. 56-11395, for example.
The radiation image recording and reproducing system of the type described above is of greater practical advantage than conventional radiographic systems using a combination of an intensifying screen and an X-ray film in that images can be recorded in a wide range of radiation exposure. More specifically, it is known that the amount of light emitted from a stimulable phosphor upon stimulation thereof is proportional in a highly wide range to the amount of radiation to which the stimulable phosphor has been exposed. Therefore, even if the amount of radiation to which the stimulable phosphor is exposed varies widely under various conditions, radiation images free from such exposure variations can be obtained by selecting a suitable read-out gain in the photoelectric transducer for reading and converting the emitted light into an electric signal, and processing the electric signal into a visible image on a recording medium such as photographic film material or on a display unit such as a CRT.
The radiation image recording and reproducing system is capable of processing a converted electric signal to produce a visible image on a recording medium or a display unit so that the radiation image can well be observed for diagnostic purpose. In this system, the stimulable phosphor sheet does not serve as a final image recording medium, but as a temporary image storage medium for eventually transferring images to the final recording medium or display unit. Therefore, the stimulable phosphor sheet can be used repeatedly, and is economical and convenient if in repetitive use.
To reuse the stimulable phosphor sheet, the remaining radiation energy on the stimulable phosphor sheet after the radiation image has been read out by stimulating rays is discharged by exposure to light, and the stimulable phosphor sheet is employed again for recording a radiation image thereon. The erasure of the irradiation energy from the stimulable phosphor sheet is disclosed in U.S. Pat. No. 4,400,619, for example.
The image erasure unit has erase light sources capable of irradiating the stimulable phosphor sheet with a high illuminance for substantially thoroughly discharging any remaining radiation energy from the sheet. In order to erase the remaining image information completely and in a short time from the phosphor sheet with the erasure light, an increased number of erasure light sources and an increased amount of erasure light should be employed to generate intensive erasure light. The increased number of erasure light sources and the increased amount of erasure light, however, tend to heat the image erasure unit excessively, resulting in damage to the image erase unit, the sheet, and the surrounding components.
As disclosed in U.S. Pat. No. 4,350,893, the stimulable phosphor sheet comprises a a support made of paper or a high polymeric organic material such as polyethylene terephthalate, and a phosphor layer deposited on the support. The phosphor layer is composed of a binder made of high polymeric organic material such as nitrocellulose, and stimulable phosphor particles dispersed in the binder. A transparent protective layer is deposited on the surface of the phosphor layer which is opposite to the support for physically or chemically protecting the phosphor layer. The protective layer is also made of a high polymeric organic material such as polyethylene terephthalate. Since the stimulable phosphor sheet is composed of organic materials that are easily susceptible to thermally induced deformation and/or property modification, thereon, when subject to excess heat from the erase light sources, the stimulable phosphor sheet is apt to be deformed and/or modified, and hence cannot be reused as desired. Inasmuch as the image erasure unit is employed for erasing a remaining radiation image from the stimulable phosphor sheet after the radiation image information has been read therefrom, the image erasure unit should preferably be assembled in the radiation image read-out device. In order to allow the image erasure unit to be easily installed in position and also to make the entire system compact, it is necessary that the image erasure unit itself be small in size. The applicant has already proposed such a compact image erasure unit of the box shape including a casing accommodating erase light sources and feed means disposed within or without the casing for feeding the stimulable phosphor sheet to a desired position (see U.S. pat. application No. 740,459).
The proposed box-type image erasure unit is however disadvantageous in that the stimulable phosphor sheet is more likely to be adversely affected by the heat given off by the erase light sources.